7mm modelling

Gn15 is a relatively new departure from my principle modelling scale of over 40 years, namely 7mm. This began when I joined the Twickenham & District MRC soon after starting my first job and I fell-in with the narrow gauge group. I had no idea what NG was at first, except it was wonderful. After working on the new O-16.5mm layout, I was then inducted into a private group who operated the Cottesmore Light Railway and that 5-man team have met weekly, ever since, although now we are only three. There was a personal departure into O-9 in the form of the Belfield Hall Estate Railway (still 7mm scale) and another into 16mm Garden Railways - both very satisfying. But I returned to O-16.5 when the weekly modelling group decided to 'revive' a portion of the CLR layout owned by John Langridge - namely Worton Court. All eager to work on a new project it has gone well, but for me, working on the fiddly rolling stock itself was not very attractive. However, the developing Gn15 interest meant I was also working on 16.5mm track and running gear even if the bodies were much larger (13.5mm/ft - almost twice the scale of 7mm). I then started overhauling long-unused stock and eventually, new models began to arrive...

Railcar - I had started buying HO American bogie chassis as they weren't too expensive and ran so well and both Gn15 and O-16.5 models came to mind. A search through books together with a Google image search was undertaken for a prototype with a view to making a 7mm passenger railcar - maybe a Lisbon-type tram. However, an attractive WD unit from the Longmoor Light Railway was discovered that offered an easy re-entry into 7mm scale. The vehicle was 4-wheeled Drewry Railcar which was redesigned for the model as a bogie version with compartments for goods and passengers. (A similar 4-wheel, but quite long Drewry railcar ran on the Weston, Clevedon and Portishead Railway - photo 3). The totally plasticard build went quite well and was ultimately kept in military livery, representing a permanent-way vehicle for the newly opened preserved Worton Court Railway. This was soon augmented by a track carrying bogie wagon complete with scratch-built portable track.

Bogie diesel - Geoff, our host for the group sessions, made a conversion of a Dagenham boxcar diesel based on a Bachmann GE44 bogie chassis - the shortest US bogie switcher. Impressed with its neat size and smooth running, I bought one on eBay, but was then torn between a Gn15 or 7mm model. However, the common problem of cracked wheel-drive gears started to appear and the project halted until a second chassis was purchased. This time, 7mm beckoned and a diesel based on 'Carnegie' (ex Woolwich Arsenal/Bicton Gardens) was created. New dummy bogie overlays were made using Slaters tender axleboxes. The grilles were eventually fabricated from plasticard rod.

New gears - When the wheel-drive gears started to show signs of cracking after the chassis was dropped, consideration had to be given to either a method of repairing or sourcing replacement gears to ensure the new model would have a decent working life. To track the correct gears, time was given to learning about gear specifications, which soon led to thoughts of 3D printing. YouTube tutorials on involute gear drafting led to a viable 3D model, which was printed by Shapeways in Holland. Individual gears are too small for printing (6mm dia.) so a set of four on a sprue was created. One of the bogies from the first, badly affected chassis was fitted with the new gears and, much to my surprise, they worked perfectly. As the range of plastics is considerable, the unit is being continuously test run to see how the chosen plastic stands up to use.